Disk drives are a type of information storage device that store information on one or more spinning disks. Other types of information storage devices include, for example, magnetic tape drives which retrieve stored information on magnetic tape (e.g. linear tape drive, helical scan tape drive). There are several types of disk drives. For example, there are so-called floppy disk drives, which store information on removable magnetic disks. There are also optical disk drives, which typically retrieve information stored on removable optical disk media. Magnetic hard disk drives typically store information on non-removable rigid magnetic disks. Also for example, there are magneto-optical disk drives, which share some of the characteristics of optical disk drives and magnetic hard disk drives.
All types of disk drives typically include a disk drive base, to which a spindle motor and head (or lens) actuator are affixed. The disk drive base may be cast of aluminum, for example to meet cost constraints. It is known in the art that it may be advantageous to include an arcuate shroud wall closely around the outer diameter of the disk(s), as a feature of the disk drive base, to reduce or attenuate dynamic excitation of certain disk drive components (e.g. disks, head stack assembly).
Another structure that may be included in a disk drive for this purpose, is a stationary plate fixed to the disk drive base and positioned partially between co-rotating disks, when the disk drive includes more than one disk. Such a stationary plate may sometimes be referred to as an “anti-disk” or a “disk damping plate.” The anti-disk may be fabricated from stainless steel, for example to better control dimensions and to obtain adequate rigidity. In that case, and if the disk drive base is fabricated from aluminum, then there will be a mismatch in the coefficient of thermal expansion by the two structures.
The present inventors have experimentally determined that during temperature changes, for example when the disk drive starts operation and warms, the aforedescribed differential expansion may cause stress to build where the lowermost anti-disk is attached to the disk drive base. They have also learned that such differential expansion stress may be partially relieved by a sudden earthquake-like slippage between the attached parts (i.e. “popping events”), which can generate an undesirable shock wave or vibration in the disk drive. If that happens during the performance of data read or write operations by the disk drive, then consequent relative movement of disk drive internal parts (e.g. head stack assemblies) may result in read or write errors (e.g. off-track write). Such problem may become even more important in the future, as data track density (i.e. tracks per inch) on the disk is projected to increase.
Therefore, there is a need in the art for a disk drive having an improved anti-disk structure to reduce or prevent thermally induced shocks, and also having a cost that is acceptable for the high-volume manufacture of inexpensive disk drives.